U.S. Pat. No. 5,423,444 discloses a plastic closure for a container having an externally screw threaded neck, the closure including a top portion and an internally threaded skirt. The closure has an annular sealing rib which projects downwardly from the underside of the top portion. The rib includes a first, substantially cylindrical portion contiguous with the underside of the top portion and lying adjacent to or abutting with the skirt and a second frusto-conical portion contiguous with the end of the first portion distal to the underside of the top portion and extending radially inwardly to a circular free edge. During threaded attachment of the closure with the neck the second frusto-conical portion will be engaged by a free end of the neck and folded back against the first substantially cylindrical portion of the rib to form a gas tight seal between the neck of the container and the closure.
U.S. Pat. No. 5,609,263 discloses a variant of the above closure in which there is at the free end of the second portion of the rib a thick seal ring of substantially circular cross-sectional shape. The rib and the seal ring are dimensioned to engage the free end of the neck when the closure is threaded onto the neck such that when the neck is fully screwed into the closure its free end crushes the seal ring directly against the inside surface of the top portion of the closure.
The present invention is directed to two arrangements of closure that improve the sealing ability of closures of the type identified in the abovementioned prior art.